1. Field of the Invention
The present invention generally relates to a contactor for electronic products and, more particularly, to a contactor for contacting electrodes of a semiconductor device to achieve a conductive connection so as to examine the semiconductor device such as a large-scale semiconductor integrated circuit (LSI) and a manufacturing method of such a contactor.
In recent years, manufacturing technology of a semiconductor substrate or the like has accomplished remarkable development. In connection with the development, circuit patterns of semiconductor devices such as an LSI have been changed to a fine structure, and an increase in the number of terminals and miniaturization of terminals have also been progressed with remarkable speed.
Moreover, high-density mounting is also required for electronic equipment using a semiconductor device. For example, the number of portable devices that require a small size and high performance, such as a mobile telephone, a mobile personal computer or a video-equipped camera, has increased rapidly. Moreover, a demand for a highly efficient computer, which minimize a distance between adjacent LSIs so as to guarantee a high-speed operation, has also increased rapidly.
For this reason, the form of shipment of semiconductor devices such as LSIs that the LSI chips are delivered with guarantee of its function has been increasing. Such a form of shipment is referred to as known good die (KGD). Moreover, the number of shipments of the chip-size package (CSP), which is a semiconductor devices packaged in the same size as the LSI chip, has also been increasing rapidly.
In the above-mentioned situation, in order to examine semiconductor devices such as LSI, a supply of contactors, which can make reliable electric contact with many terminals formed as a part of fine circuit patters, has become indispensable.
Moreover, in view of an increase in efficiency of an LSI test, a demand has become large for performing all tests including a final test (FT) and a burn in test (BI) as a wafer on which a plurality of LSIs are formed in the LSI manufacturing process.
The full test in a wafer state is effective in maintaining good handling efficiency rather than testing in the state where chips are separated from each other. That is, although the versatility of handling equipment will be lost if the sizes of chips differ from each other, bulk conveyance can be made in the wafer state since an outer configuration of wafers is standardized.
Moreover, there is an advantage that information regarding defective chips can be managed according to a wafer map. Furthermore, a manufacturing process of the wafer level CSP, of which development has been progressing in recent years, is manageable in the wafer state up to an assemble process. For this reason, if a test in the wafer state is realized, chips can be handled in the wafer state throughout the process from a wafer process to packaging (assembly) and testing, thereby achieving an efficient manufacturing process of LSI.
Therefore, it is desirous to develop a contactor which can contact many fine-structure pins of an LSI with corresponding terminals of a test board.
2. Description of the Related Art
Conventionally, the following contactors are used as a contactor for an LSI examination: 1) a contactor using a needle-type mechanical probe; 2) a contactor using a membrane probe; and 3) a contactor using an anisotropic conductive rubber.
1) Contactor Using a Needle-type Mechanical Probe
1-1) Cantilever Probe
The contactor using a cantilever-type mechanical probe is formed by arranging needles (formed of a tungsten wire or the like) in positions on a contactor substrate corresponding to positions of terminals of an LSI to be tested. Generally, each needle is constituted so as to extend toward a terminal of the LSI in an inclined state with respect to the LSI.
The contactor using the cantilever probe is used mainly for a peripheral-terminal LSI for a bare wafer. However, such a contactor has a large length of each needle (generally, 20 mm or more), and it is difficult to be used for an LSI having area array terminals. Moreover, since roots of the probes are arranged around one LSI, contact electrodes for an adjacent LSI cannot be formed.
For this reason, a perpendicular probe has attracted attention in recent years. The perpendicular probe is a probe in which contact electrode pins are arranged at the same pitch as LSI terminal so as to acquire a contact action and a contact force sorely by bending of the probe in a vertical direction.
1-2) Spring Probe
A coil spring is used as a contact electrode pin. For example, coil springs are arranged and resin or rubber is filled therebetween so as to connect mutually. The interval of adjacent coil springs is determined by a pitch of terminals of an LSI and a diameter of the coil springs. That is, the interval of adjacent springs is a value obtained by subtracting the diameter of the coil springs from the pitch of the terminals of the LSI.
2) Contactor Using Membrane-type Probe
A membrane-type probe is formed as a film-like circuit board having a metal projection (herein after, referred to as a bump) as a contact electrode for probes. For example, a wiring layer is formed in a flexible thin film insulation substrate (polyimide substrate, etc.), and projections (bumps) are formed in the portion equivalent to the contact electrode terminal parts of the wiring layer by plating etc. As for this method, a contact electrode is beforehand formed on an insulating substrate. There is no problem resulting from the interval of adjacent contact electrodes like a mechanical probe.
3) Contactor Using an Anisotropic Conductive Rubber
An anisotropic conductive rubber is formed by embedding materials (metal wire etc.), which are conductive only in a direction of thickness, in an insulating material such as rubber.
I) The needle-type mechanical probe has the following demerits.
a) Since needles are formed one by one on an individual needle basis, a manufacture cost of the contactor is high.
b) Since needles are attached to a contactor substrate individually, there is a limit in accuracy of positioning of the needle tip.
c) When needles are inclined, there is a limit in arrangement of the needles, and, thus, it is difficult to make the contactor to simultaneously contact electrodes of a plurality of LSIs.
d) In the case of a coil spring type, the interval of adjacent coil-springs is very small when the coils springs are arranged at a small pitch, and, thus, it is difficult to manufacture a structure itself in which the coil springs are arranged and supported in one piece.
II) The membrane-type probe has the following demerits.
a) Each contact electrode cannot move freely. Each contact electrode is embedded into the insulating substrate, and the movable range each contact electrode is small. Moreover, each contact electrode is formed of a metal bump which has less flexibility. For this reason, if there is variation in the height of the bumps, there is a problem in that a low bump does not make a contact or causes insufficient contact may occur.
b) Since the bump forming each contact electrode is generally formed by accumulating metal plating layers, it takes a time for manufacturing the contactor and the manufacturing-cost is high.
III) The anisotropic conductive rubber has the following demerits.
a) A service life is short. Especially, when using at a high temperature, the contactor may be used only 20 to 30 times due to plastic deformation of a rubber part, and only once in the shortest case.
b) Since it is difficult to embed conductive materials into rubber at a small pitch, it cannot be applied to an LSI having electrodes of a small pitch. The pitch of the electrodes to which the anisotropic conductive rubber can be applied is about 150 μm.
Furthermore, since the total number of terminals of all LSIs on a single wafer may reach a few ten thousands in the contactor used for simultaneous wafer-level contact, there are following problems common to the above-mentioned types of contactors.
i) A surface of an LSI terminal (mainly an aluminum pad and a solder bump) is covered by an oxidization film. For this reason, it is desirable to perform a wiping operation, when the contactor makes a contact so as to remove the oxidization film. The wiping operation is an action to wipe a contact surface by sliding a contact tip of a contactor on the contact surface. Among the above-mentioned probes, the probes other than the cantilever-type probe basically deform in a vertical direction and cannot perform the wiping operation.
Moreover, since the terminal size is small, a distance of slide in the wiping operation is preferably as small as possible. Thus, it is necessary to find out the minimum wipe distance while maintaining a sufficient contact pressure. In order to attain this, it is necessary to develop a contactor which can control a contact pressure and a wipe distance separately.
ii) The pressure for pressing a contact electrode against the terminal of LSI is very large.
In the method of the above-mentioned conventional method, a pressure more than 0.1 N (about 10 g) per one terminal is needed, and, thus, when there are about hundred thousand terminals in an entire wafer, a pressure of about 10000 N (about 1000 kg) is needed. Since it is difficult to apply a pressure uniformly to whole terminals due to variation in the height of the contact electrodes, there may be a case in which an excessive pressure is applied to a specific terminal. Moreover, if there is no equipment which receives a total pressure, a wafer may break or bend, which may cause a damage of circuits on the chip.
iii) A position gap occurs due to a difference in thermal expansion coefficient. The LSI wafer is made from silicone in many cases, and the thermal expansion coefficient of silicon is about 3 ppm. However, since the insulating substrate of the above-mentioned contactor is formed of a resin or rubber material, the thermal expansion coefficient thereof is about 13-30 ppm. Therefore, although the contactor is accurately in contact with the LSI terminals at a normal temperature, the contact position of the contact electrodes may shift, when the contactor and the LSI are exposed to a high temperature such as in a BI test, due to a difference in the thermal expansion coefficient between the insulating substrate material and the silicon material of the wafer. Thus, there is a possibility that the contact electrode disengages from the LSI terminal or contacts an adjacent terminal. In a case in which polyimide is used for the insulating substrate material which has a thermal expansion coefficient of about 13 ppm, when a 8-inch wafer (a radius is about 100 mm) is used, if the wafer is heated up to 125 degrees C., a position shift of about 100 μn may occur in the terminal position near an outermost circumference of the wafer even when the contactor is accurately positioned at a normal temperature.